A conventional pixel sequential rasteriser 1000, for graphics rendering, is shown in FIG. 10. The rasteriser 1000 comprises an instruction execution module 1001, an edge tracking module 1002, a level activation module 1003, a pixel color generation module 1004, a compositing module 1005 and a pixel output module 1006. Each of the modules 1001-1006 are typically implemented as one of more computer software modules executing within a computer system. Each of the modules 1001-1006 may alternatively be implemented in dedicated hardware such as one or more integrated circuits.
In such a rasteriser 1000, the instruction execution module 1001 is used for configuration of the computer system to process a printing job. Edges of graphical objects (or “objects”) are tracked between lines by the edge tracking module 1002, and object edge positions are passed to a level activation module 1003. The level activation module 1003 determines activation and visibility of graphical objects for runs of pixels between edges of the objects based on level activation information stored in level activation table. The output of the level activation module 1003 is a set of commands for drawing each run of pixels. The commands are provided with colour data by the pixel colour generation module 1004, and are performed by the compositing module 1005, the resulting pixel colours being output by the pixel output module 1006.
A need exists for a more efficient rasteriser for use in rendering a graphical object on a page.